The present invention relates to an apparatus for reverse redrawing of a cup in a system for producing the so-called two-piece metallic can having an integrated can body and can bottom by drawing or both drawing and ironing.
The two-piece metallic can is usually produced by blanking a disc from a metallic sheet, drawing the disc into a cup, and redrawing the cup, and, if necessary, ironing the cup, thereby obtaining a desired can height. Among these steps, the redrawing of a cup is carried out according to the following reverse redrawing method shown in FIG. 1. That is, a cup 1 is crowned on a die ring 2 so that the inside surface of body portion 11 of cup 1 can be in contact with the outside surface 24 of ring body portion 21 of die ring 2, and the bottom of cup 1 is pressed into the inside of die ring 2 by a punch 3 so that the face side and the back side of cup 1 can be reversed, whereby the diameter of cup 1 is reduced. When the cup is reversingly redrawn according to said method, it is known that longitudinal wrinkles 13 are developed at the open end 12 of reversingly redrawn cup 1', as shown in FIG. 2, unless a press device or a blank holder for pressing the body portion of the cup 1 on an upper surface of the die ring, is used in the case the thickness of body portion 11 of cup 1 is thin.
One example of the well known press device is shown in FIG. 3. and the press device has pressure ring 4 of a hollow cylinder being provided concentrically with punch 3 and having a lower end 41 with a concavely curved surface matching the convexly curved surface of upper end 22 of die ring 2 and an inner diameter substantially equal to the outer diameter of punch 3. Pressure ring 4 is made to move down toward die ring 2 in a vertical direction before punch 3 moves down and holds cup 1 between lower end 41 and upper end 22 of die ring 2.
Another press device is shown in FIG. 4. A horizontally movable press device comprised of a plurality of horizontally movable members 5 is provided at a definite distance of upper end 22 of die ring 2. When cup 1 is pressed onto die ring 2, tip end 12 of body portion 11 of cup 1 slides down against slope 51 on horizontally movable members 5, and thus the members 5 of press device are pushed away outwardly, and then cup 1 is crowned on die ring 2. After the crowning of cup 1, the members 5 of horizontally movable press device as pushed away outwardly get together against toward the center and recover the original shape. At that time, the members 5 are positioned as near as possible to the upper surface of bottom 15 of cup 1 and functions to prevent development of wrinkles.
However, the conventional press devices shown in FIGS. 3 and 4 are members of a vertically or horizontally reciprocating movable type, and thus have a complicated mechanical structure to move said members.
Furthermore, the conventional press devices are more liable to have damages or troubles due to mechanical wearing or repeated fatigue during the reciprocating movements, and thus are not suitable for high speed processing.
Furthermore, the press device shown in FIG. 3 has a particularly complicated mechanical structure, and thus has such disadvantages that much labor and time are required for replacement of die or adjustment, and the press device shown in FIG. 4 has such disadvantages that the drawing and ironing strokes are increased corresponding to the thickness of the members of the press device, and it takes more time in reciprocating the drawing and ironing punch, and when cup 1 is crowned onto die ring 2, the members 5 of press device are pushed away outwardly by tip end 16 of body portion 11 of cup 1, and sludge is liable to be deposited on the outer surface (as shown in FIG. 4) of cup 1 at that time, and when the cup is redrawn as such, sliding scars appear on the inner surface (the reversed outer surface) of the resulting redrawn product, and furthermore such a disadvantage that, when the members 5 of press device are pushed away outwardly by the tip end of cup body portion, the cup body portion may be deformed.